Journal of the London Mathematical Society Advance Access originally published online on September 10, 2009
Journal of the London Mathematical Society 2009 80(3):603-626; doi:10.1112/jlms/jdp046
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© 2009 London Mathematical Society
Banach Lie algebras with Lie subalgebras of finite codimension have Lie ideals
Department of Computing, Communications Technology and Mathematics
London Metropolitan University
166-220 Holloway Road
London
N7 8DB
United Kingdom
Department of Computing, Communications Technology and Mathematics
London Metropolitan University
166-220 Holloway Road
London
N7 8DB
United Kingdom
shulman_v@yahoo.com
Institute of Mathematics and Mechanics
National Academy of Sciences of Azerbaijan
9 F. Agayev Street
Baku AZ1141
Azerbaijan
yuri.turovskii@gmail.com
This paper continues the work started in [E. Kissin, V. S. Shulman and Yu. V. Turovskii, Banach Lie algebras with Lie subalgebras of finite codimension: their invariant subspaces and Lie ideals, J. Funct. Anal. 256 (2009) 323–351.] and is devoted to the study of reducibility of an infinite-dimensional Lie algebra of operators on a Banach space when its Lie subalgebra of finite codimension has an invariant subspace of finite codimension. In addition to the tools developed in the above paper; filtrations of Banach spaces with respect to Lie algebras of operators and related systems of operators on graded Banach spaces, the present paper introduces and studies some new concepts and techniques: the theory of Lie quasi-ideals and properties of Lie nilpotent finite-dimensional subspaces of Banach associative algebras. The application of these techniques to an operator Lie algebra
shows that, under some mild additional assumptions,
is reducible if its Lie subalgebra of finite codimension has an invariant subspace of finite codimension. This, in turn, leads to the main result of the paper: if a Banach Lie algebra
has a closed Lie subalgebra of finite codimension, then it has a proper closed Lie ideal of finite codimension. Moreover, if
is non-commutative, then it has a characteristic Lie ideal of finite codimension, that is, a proper closed Lie ideal of
invariant for all bounded derivations of
.
2000 Mathematics Subject Classification 47L70, 47A15 (primary), 47L10 (secondary).
The support received from INTAS project No 06-1000017-8609 is gratefully acknowledged by the third author.
Received September 4, 2008; revised May 27, 2009; published online September 10, 2009.